1. Field of the Invention
The present invention relates to a suspension arrangement for a hydraulic elevator.
2. Description of the Background Art
At present, conventional hydraulic elevators are implemented as rucksack-type elevators in which the elevator car is mounted on a supporting frame resembling a rucksack. As to their suspension, these elevators are either of a direct-acting or an indirect-acting type. Direct-acting elevators of normal construction without an expensive telescopic cylinder are only applicable in low-rise buildings where the elevator only serves one or two floors. Therefore, most hydraulic elevators employ an indirect-acting type of suspension. Such elevators usually have a hoisting height of 3.5-15 m, corresponding to 2-6 floors. The maximum hoisting height is about 20 m. In an indirect-acting elevator, a hoisting rope attached to a fixed column is passed over a diverting pulley mounted on top of the piston and further to the car frame supporting the elevator car. Due to this roping, the car travel equals twice the stroke of the piston, which is why this type of suspension is termed 2:1 suspension.
However, this widely used suspension system has certain serious drawbacks. First, since the length of the cylinder (and the piston inside it) equals at least half the entire hoisting height, difficulties are encountered in transporting such a long cylinder into the elevator shaft. The cylinder is usually brought into the shaft via its door opening, in which case the cylinder may be at most about as long as the guide rail bar, i.e. about 5 m. This limits the hoisting height to 10 m, corresponding to four floors.
When larger hoisting heights are to be achieved, the cylinder has to be hoisted into the shaft via the top of the shaft. However, this is only possible at an early stage of the construction work, and it is necessary to schedule the transport and hoisting of the cylinder into the shaft accordingly. This causes extra work and expenses. Moreover, the cylinder has to be protected in the shaft during construction, and it is always more or less of a hindrance to other work.
Another solution applied in the case of large hoisting heights is to use an extendable cylinder. In this case, the cylinder is composed of two sections which are only joined together in the shaft. However, because of the threaded joint, the cylinder has to be manufactured from a thicker tube than a jointless one. Because of the joint, the manufacture of the cylinder and especially its final grinding is an elevator- and cylinder-specific and expensive job. The testing of the cylinder also requires special arrangements, and joining the cylinder sections and installing the cylinder in a narrow and dirty space is difficult and expensive. A jointed cylinder costs at least one and a half times as much as a jointless one.
Another limitation in the case of 2:1 suspension, in addition to the problem of moving the cylinder into the shaft, is the risk of buckling of the piston tube at larger hoisting heights. This limits the hoisting height and makes it necessary to increase the thickness of the wall of the piston tube. However, this increases the weight of the piston, thus reducing the usable hoisting capacity of the cylinder. Moreover, due to the material costs, this is an expensive solution. Another way to solve the buckling problem is to use reinforcements to prevent buckling, but this also involves additional costs.